The left has united behind Ed Miliband. Now he has to be bold

The foundation has been laid, the policies brewing. Labour now needs its leader to be optimistic and radical if it is to win

Impatience in Labour ranks is understandable: where are the new policies? Ed Miliband seems to do or say something clever, but then fall silent.' Photograph: Daniel Pudles for the Guardian Daniel Pudles/Guardian

It suits Labour's enemies to imagine that the letter from thinktanks in yesterday's Guardian was a "savage" attack on Ed Miliband. On the contrary: in an unprecedented display of unity, groups all the way from the trade unionists of Class to Fabians and Progress called for what Miliband himself spelled out in his recent Hugo Young speech. The aim is to stiffen his sinews to follow his own radical instincts.

Don't play safe, don't rely on Tory unpopularity to creep over the line, but earn a mandate for radicalism. This goes with the grain of a leader who has denounced irresponsible capitalism, defied Murdoch, damned the energy companies, helped stop the UK and US bombing Syria, and shown how shrinking pay undermines the economy. No surprise his team sounds encouraged, not threatened, by the party calling for "transformative change."

Any leader is besieged by advice. Access to his ear to urge this or that is sought by all. Some say forward! Others bring warnings. Alarming focus groups depict a backward-looking, grudging populace that detests all politics. Some tell him people don't like his face, don't see him as prime minister (they didn't see Heath, Thatcher or Major as PM either until they reached No 10). Every morning Miliband is beset by that hostile spread of Britain's 80% Tory press, ratcheting up its assault as the election nears. A BBC disoriented by that unbalanced voice and cowed by attacks on itself, too often fails to locate the genuine centre-ground. Miliband does keep his nerve when all about are losing theirs, but who wouldn't sometimes be daunted in the watches of the night?

Don't underestimate the significance of this letter from the thinktanks, with its optimistic belief that Labour can be bold, despite few funds for spending. Were it just right- or left-leaning thinkers, the story would be split and panic. Instead – plainly bewildering to some commentators – here is unaccustomed unity of purpose. This was not, as some gleeful critics suggest, an instant response to the government's budget bounce. It took time for Neal Lawson of Compass to assemble this breadth of agreement to principles of decentralisation, devolution, green growth and accountability. Laugh, if you will, at the earnest wonkery of the abstract intellectual language, but doorstep-ready practical policies don't work if they are pick-and-mix random offers without ideas signifying a party's wider purpose.

Jon Cruddas, the head of Labour's policy review. Photograph: Karen Robinson For The Observer/Karen Robinson

Why write this letter now? Jon Cruddas has been a long time brewing his policy review, but bundles of policies are about to emerge ahead of Labour's National Policy Forum at the end of July. This is the moment to urge imagination.

The strongest theme is devolution to councils and other local bases. Local government is almost derelict, yet Labour has seen a flowering in the cities and boroughs it controls, often led by more enterprising, lively minds than in Westminster. Places such as Manchester, Newham, Lewisham and Liverpool buzz with desire to do things better. Taking policies out of Whitehall silos makes it easier to integrate budgets locally. Devolving housing, education, employment, health and nurseries to local decision-making may release a new generation of political energy.

But you can see why some take fright, alarmed by postcode lotteries. Oppositions fall in love with localism because they control most councils, but once in power, governments lose that local control. How would Labour feel about all this freedom devolved in future to swaths of newly elected Tory councils to cut, privatise or ignore Westminster egalitarian social policies? Cameron, too, promised devolution, but trusting the people can be difficult when they insist on voting the wrong way.

Impatience in Labour ranks is understandable: where are the new policies? Miliband seems to do or say something clever but then fall silent. Some grumble there's been more agreeing with Tory cut-throat spending limits and welfare caps than striking out in new directions. But they won't have to wait long. Talking to those close to the policy process, the aim is to lay out a carpet of ideas one by one. Outlines are taking shape, with setting women free at the core. That means a universal social care service, paid for with hypothecated funds. That means universal childcare at last provided directly in good free nurseries, not from complex subsidies and rebates. Local education boards will make sense of school provision. Expect major new house building and infrastructure with between £35bn and £50bn of capital, councils free to borrow.

How do you cap welfare? Only by holding down housing benefit through controlling rents, only by raising pay to keep down tax credits. Highly popular would be capping the profits that private companies can make from public contracts. Rail franchises may fall back to the state, after the success of the East Coast line. Green growth will be back in favour. What's encouraging is that all this emerges from all sides, the same from Patrick Diamond and Neal Lawson, as if left/right in Labour had all but blended into one. Defying history and gravity, surely that can't last.

What are these forces of conservatism the letter fears? Ed Balls is prime suspect, the Treasury brief inclined to be a blocking No, wary of letting councils borrow. But the Cruddas team denies it hotly, their plans closely knitted with Balls's zero-base spending review.

No, the drag on boldness is more nebulous, fearful of the shadows of their past. Unable to shake off the calumny that they broke the world's banks, Labour must handcuff itself to credibility and responsibility. Offering anything at all sounds feckless. But in truth, Labour has no safe haven. If cutting the deficit is all voters want, they won't vote Labour. The only hope is daring and lifting people's sights and making a break from a dismal future where everything is destined to shrink and shrivel.

• This article was amended on 26 March 2014. An earlier version incorrectly described Tony Blair as president of Progress.